1. Field of the Invention
The present invention relates to magnetic random access memory (‘MRAM’), and in particular to an improved MRAM having a similar structure to folded bit line DRAM having a unit cell area of 8F2, wherein lines are arranged in a way that only one write word line is required for every two word line and only one ground line is required for every two bit line.
2. Description of the Background Art
Most of the semiconductor memory manufacturing companies have developed the MRAM, which uses a ferromagnetic material as one of the next generation memory devices.
The MRAM is a memory device for reading and writing information wherein multi-layer ferromagnetic thin films is used by sensing current variations according to a magnetization direction of the respective thin films. The MRAM has a high speed and low power consumption, and allows high integration density due to its unique properties of the magnetic thin film, and also performs a nonvolatile memory operation such as a flash memory.
The MRAM embodies a memory device by using a giant magneto resistive (GMR) or spin-polarized magneto-transmission (SPMT) phenomenon generated when the spin influences electron transmission.
The MRAM using the GMR phenomenon utilizes the fact that resistance remarkably varies when spin directions are different in two magnetic layers having a non-magnetic layer therebetween to implement a GMR magnetic memory device.
The MRAM using the SPMT phenomenon utilizes the fact that larger current transmission is generated when spin directions are identical in two magnetic layers having an insulating layer therebetween to implement a magnetic permeable junction memory device.
FIG. 1 is a schematic diagram illustrating a conventional MRAM and FIG. 2 is a cross-sectional diagram illustrating the conventional MRAM of FIG. 1.
Referring to FIGS. 1 and 2, the conventional MRAM comprises a transistor and an MTJ cell 80. The MTJ cell 80 is connected to a bit line 90 and to a drain region 30 of the transistor through a connection layer 60 and a contact plug 50. The MRAM further comprises a write word line 70 for storing information by varying the magnetization direction of MTJ cell 80. A gate electrode 20 of the transistor serves as a word line for reading the data. A source region 40 of the transistor is connected to ground through a ground line 45.
The conventional MRAM, contrary to a DRAM, requires four independent lines including the ground line, the word line, the write word line and the bit line.